In a multiprogramming, virtual-memory computing system, many processes compete for the main storage page frames and CPU's of the real system. It is customary to define a subset of these processes called the “multiprogramming set” (MPS), and to allocate resources only to those processes currently in the MPS. Each process remains in the MPS for a limited time and is then demoted. The system paging manager controls the size of the MPS; it allocates the available page frames among the processes in the MPS and fetches appropriate pages into the page frames.

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